The present invention relates to orthodontic brackets, and more particularly, an orthodontic bracket having an improved bonding base, and a method for making same.
In the practice of orthodontia, orthodontic brackets are typically bonded directly to the teeth of a patient. It has always been important to provide good bonding between the orthodontic bracket and the tooth. Over the years, many improvements have been made to metal orthodontic brackets and the adhesive used to bond the metal brackets to the teeth. As a result, the bonding of typical prior art metal brackets to the teeth has reached generally accepted values. Recently, aesthetic brackets have become extremely popular. Typically, these aesthetic brackets are made of materials other than metal, and typically are substantially transparent, or tooth-like in color. For example, recently, orthodontic brackets made out of single crystalline material and strengthened glass have been suggested. While these new materials have offered many possibilities in providing brackets with an aesthetically pleasing appearance, the task of bonding these brackets to the tooth has become much more complicated. Due to the hard smooth surface condition of these materials, it is substantially more difficult to provide a high strength bond between the bracket and the tooth. One method of improving the bonding strength between a bracket made of single crystal alumina and a tooth is suggested in U.S. Pat. No. 4,681,538. However, the method disclosed in this patent requires special handling and care in order to obtain acceptable bonding strength. Additionally, a serious problem with such chemically treated adhesion systems of the prior art is that when these brackets are removed or broken from the tooth, there is a high risk that a portion of the tooth enamel will also be removed.
It has also been suggested in the prior art the provision of undercuts on the base of crystalline or ceramic brackets. While such undercuts have improved bonding strengths, these undercuts do not provide the same strength typically found with prior art metal brackets. Another problem encountered with adhesives for aesthetic brackets is that certain adhesives have been found to detract from the transparent or translucent characteristics of the bracket.
It has also been suggested that the application of a substantially monolayer of particles of substantially uniform size to the bonding base of an orthodontic bracket as set forth in Applicant's copending patent application, Ser. No. 241,193, filed Sep. 7, 1988. While this has proven satisfactory in providing desired bond strengths, the method employed requires the brackets to be heated to high temperatures so as to diffusion bond the particles to the bracket. This heating process requires time and adds further cost to the product. Additionally, diffusion does not work well for materials such as glass, as it tends to damage the particles and/or the bracket during the heating process.
Applicant has invented an improved orthodontic bracket and method of making same wherein acceptable bonding strengths are obtained while maintaining the attractive aesthetic qualities of the bracket and additionally minimizes the possibility of removing enamel from the tooth.